1. Field of the Invention
The present invention relates to an ultrasonic motor and to a pressing mechanism of an ultrasonic vibrator.
This application is based on Japanese Patent Application No. 2007-010336, the content of which is incorporated herein by reference.
2. Description of Related Art
Ultrasonic motors, which are compact and have high torque, long stroke, and high resolution compared to electromagnetic motors, are commonly used in the related art.
Ultrasonic motors are motors for driving a driven member with a friction force that is generated between an ultrasonic vibrator and the driven member by pressing the ultrasonic vibrator against the driven member. A known pressing mechanism for pressing an ultrasonic vibrator against a driven member in the related art is disclosed, for example, in Japanese Unexamined Patent Application, Publication No. HEI-11-312017.
This pressing mechanism includes compression springs which are disposed at two locations in the longitudinal direction of the ultrasonic vibrator and which have spherical faces at their ends, and set screws for adjusting the amount of compression of the compression springs. This pressing mechanism is constructed in such a manner as to balance the contact pressure between the driven member and the ultrasonic vibrator by adjusting the amount of compression of each compression spring by adjusting the amount of engagement of each set screw, and by changing the pressing force applied to the ultrasonic vibrator from each compression spring via the spherical faces.
However, the ultrasonic vibrator pressing mechanism disclosed in Japanese Unexamined Patent Application, Publication No. HEI-11-312017 merely applies the pressing forces at a plurality of locations on a surface opposite from a contact surface between the ultrasonic vibrator and the driven member; there is no mention of the driving efficiency of the ultrasonic motor at all. Accordingly, although it is possible to balance the contact pressure between the driven member and the ultrasonic vibrator by applying the pressing forces at two locations, there is a drawback in that the driven member cannot be driven with high driving efficiency.